Add function for fast modular exponentiation.
Add function for fast modular exponentiation.

The function uses GMPY's bignum arithmetic which speeds up the calculation.

masterkorp/obfsproxy,catinred2/obfsproxy,qdzheng/obfsproxy,Yawning/obfsproxy-wfpadtools,isislovecruft/obfsproxy,NullHypothesis/obfsproxy,infinity0/obfsproxy,david415/obfsproxy,sunsong/obfsproxy,Yawning/obfsproxy